This invention relates to improvements in the field of herbicidal treatment of plants. The invention involves a method of herbicidal treatment of plants whereby unwanted plants and grasses are terminated using a formulation that is highly effective to non-selectively. kill plants it contacts. More particularly, the invention relates to “knock-down” herbicide formulations that comprise a herbicidally active limonene component.
By way of background, limonene is a naturally occurring chemical found in high concentrations in citrus fruits and spices. Limonene, otherwise known as orange limonene or 1-methyl-4-(1-methylethenyl)cyclohexene or 4-isopropenyl-1-methyl cyclohexene, occurs naturally in various ethereal oils, particularly oils of lemon, orange, lime, grapefruit, caraway, dill and bergamot. It has a chemical formula of C10H16, a molecular weight of 136.2, and contains 88.1% Carbon and 11.8% Hydrogen by weight. The d-form of limonene is a liquid having a boiling point of 175.5-176 degrees centigrade.
Some limonene is prepared by extraction from plants of the mint family, a large quantity is obtained from citrus oils, which are typically 80-90% limonene, and some is obtained from pine oil. For example, d-limonene can be obtained from steam extraction of citrus peels of orange, lemon, lime, grapefruit and bergamot. Some of the extractions can contain as high as 90% d-limonene; however, to produce technical grades of d-limonene of higher purity, i.e., greater than about 95%, distillation of the oils is required. d-Limonene can also be synthesized chemically. d-Limonene has a pleasant citrus scent and it can be suitably used in any living environment.
In addition to uses as flavor additives in a. wide variety of foods and beverages and uses in perfume materials, d-limonene has also been used in household and industrial cleaning products. It is readily available from commercial sources such as Florida Chemical Company, Inc., and is available in three different grades, named untreated/technical grade, food grade and lemon-lime grade. The food grade comprises about 97% d-limonene, the untreated/technical grade about 95%, and the lemon-lime grade about 70%, the balance in each case being other terpene hydrocarbons and oxygenated compounds.
Limonene has become a valuable industrial chemical. It finds use as a solvent and cleaning agent (in the manufacture of synthetic pine oil), as an expectorant, as a wetting and dispersing agent, as a monomer in the manufacture of various polymeric resins, as a flavorant in many food products and a precursor in the synthesis of the flavorant carvone, and as a polymerization inhibitor in storage of the tetrafluoroethylene monomer used in the manufacture of polytetrafluoroethylene (PTFE). It is also used in many soaps and perfumes for its lemon-like flavor and odor. In addition, limonene is a registered active ingredient in at least 15 pesticide products used as insecticides, insect repellents, and dog and cat repellents. For example, pesticide products containing limonene are used for flea and tick control on pets, as an insecticide spray, an outdoor dog and cat repellent, a fly repellent tablecloth, a mosquito larvicide, and an insect repellent for use on humans.
Limonene is of relatively low acute toxicity taken orally. The U.S. Food and Drug Administration considers limonene Generally Recognized as Safe (GRAS) as a food additive or flavoring, and as a fragrance additive. The U.S. Environmental Protection Agency has granted limonene an exemption from the requirement of a tolerance when it is used as an inert ingredient in pesticide formulations, and when used as an insect repellent tablecloth.
Turning now to consideration of herbicides, a wide range of chemicals are used to control weeds in the agricultural industry and to control unwanted vegetation in the landscaping industry. The aim of herbicides is to prevent weeds and unwanted plants from competing with a desired crop in the case of agricultural uses, or competing with preferred vegetation in landscaping applications.
At present, there-are two main classes of herbicidal chemicals that are used in connection with terrestrial plants, which is the subject of the present invention. In particular, the herbicides are generally separated into those that have a “contact” action upon plants, and those that have a “systemic” action upon plants. Some herbicides have both a contact and systemic action on plants. Other types of herbicides act in other ways, such as, for example as soil sterilants.
Herbicides may either be selective or non-selective. Selective herbicides, for example “Treflan” (trifluralin), may be utilized for the selective destruction of certain types of grass. Non-selective herbicides such as “Roundup” (glyphosate) may be used as a general herbicide for destroying or controlling many different types of plants and grasses.
A large number of herbicides and plant hormones have been developed over the years. In the early days inorganic compounds such as sodium chlorate and sodium arsenite and various borate compounds were used. There were also developed other organic herbicides such as Nphenylcarbamate, “Randox”, and other chlorinated phenoxy compounds. In addition, industrial waste products were quite common. Later on, the hormone type weed killers 2,4-D (2,4-dichloro-phenoxyacetic acid) and 2,4,5-T (2,4,5-trichloro-phenoxyacetic acid) were developed, and have become quite common. More complicated organic weed killers and proprietary chemicals such as “Network” or “Roundup” (both glyphosates) have also been developed.
In many cases herbicides have deleterious effects. For example, they may poison beneficial crops, affect other plants or animals, and/or poison the soil. In addition, many herbicidal compositions presently on the market are highly toxic to humans and domestic animals. Most chemical herbicides are dangerous to mankind and are therefore dangerous when accidentally inhaled and/or absorbed into human and animal tissue. Because of the widespread concern of the deleterious side effects of currently available herbicides, and the problems associated with absorption and ingestion into other living matter, there is much concern as to the long-term use of complex and highly dangerous chemicals, especially when they enter into the food chain. A herbicide having lower toxicity is desirable.
There has been developed recently a relatively nontoxic herbicide which has fatty acids as its main constituents. This herbicide has a smothering effect on plants, however its efficacy is limited particularly in controlling perennial weeds. A further disadvantage is that the fatty acids are not readily carried or emulsified within an appropriate carrier fluid or solvent, which lessens its overall effectiveness due to the difficulties encountered in delivering the herbicide to plants.
It has been suggested recently that limonene can be used at a high concentration as a knock-down herbicide. In U.S. Pat. No. 5,998,335 to Selga et al., knock-down herbicidal compositions are described, one of which comprises about 95-96% by weight of d-limonene and about 4-5% of other components. The '335 patent reports that when this composition was applied to vegetation as a fine droplet spray (targeting 60-80% coverage of vegetation), most vegetation showed visible signs of stress (e.g., wilting or browning) within 2 to 24 hours of application of the herbicide. Selga et al. also reported in the '335 patent that an emulsified mixture of 60% d-limonene with water and commercial emulsifier was also tested. When this formulation was applied to vegetation as described above, most vegetation began showing visible signs of stress within 2 to 36 hours.
One disadvantage of the herbicides described by Selga et al. is that such high concentrations and volumes of limonene would be cost prohibitive and cumbersome for spraying large areas. These formulations also present practical challenges associated with effectively atomizing and spraying such oily or highly viscous compositions.
In light of the above, there is a continuing need for environmentally-friendly herbicides having increased efficiency and efficacy. The present invention addresses this need and provides a wide variety of benefits and advantages.